The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Although piston and engine technology is fairly well developed, small incremental improvements are key to making a better engine. For example, engines that incorporate aluminum or an aluminum alloy have been widely employed in recent years in order to reduce the weight of and/or improve the heat release from internal combustion engines. However, aluminum or aluminum alloys are inferior to conventional cast iron in their mechanical strength when exposed to high temperatures.
The surface strength of an aluminum alloy casting may be enhanced by casting an aluminum alloy around a metal insert of a different metal by gravity casting or die casting. However, a molten aluminum alloy cannot be bonded to the surface of a metal insert with the sufficient strength to avoid the occurrence of de-bonding and/or cracking during use. In the case of die casting, although bond strength and packing density are improved, it is difficult to prevent blistering caused by the expansion of entrapped air upon heat treatment. In addition, the use of a porous metal body or insert provides a piston head that exhibits relatively low strength. The low density of a porous metal body can cause cracks to be readily generated when attempting to form a predetermined shape in the casting operation.
Various attempts have been made to provide engine piston heads with insulation through the use of ceramic coatings, ceramic inserts, or air gaps. The purpose(s) for providing such insulating means may include raising combustion temperatures, reducing heat losses, improving engine efficiency, reducing wall quenching, and/or reducing undesirable exhaust emissions. Generally, however, insulated piston designs have not been found satisfactory because they are difficult or incapable of being manufactured, exhibit inadequate durability, or lack the level of insulation necessary to control heat flow.